1. Field of the Invention
The present invention relates to seal rings in a rotary retort heat treating furnace. The instant invention discloses seals which have a much longer useful life than those presently in use and a method of installing these seals on the rotary retort heat treating furnace.
2. Description of Background Information
Rotary retort heat treating furnaces were developed in the 1950's and are currently used to harden and temper steel fasteners and bearings. It is known that this style furnace consists of an outer shell and an inner screw chamber, or retort, which turns about a longitudinal axis, advancing product to be hardened therethrough. The operating temperatures of conventional rotary retort heat treating furnaces are approximately 1600.degree. F. The product is stirred and advanced along the length of the rotating retort until it is dropped out of the discharge end into a quick cool quench.
To prevent the steel product from reacting with regular or ambient air and consequently oxidizing, the rotary retort contains a protective atmosphere. When the rotary retort furnace was first developed they were shipped with brass seal rings. Because of difficulty in fit, those brass seals were replaced by asbestos rope gaskets.
Because of federal regulations, asbestos rope gaskets were no longer an available alternative as a furnace seal. As a result, asbestos rope gaskets were replaced by fiberglass seals. Because of the intense heat and constant wearing that these fiberglass rope gaskets are subjected to, some have a reported useful life of less than three months.
HARIG et al., U.S. Pat. No. 4,087,334, discloses a seal arrangement for a rotary drum assembly treating materials in a temperature range of 1500.degree. F and 1800.degree. F. The seals maintain a preselected pressure within the drum. The seal assembly is comprised of a rotating seal and a static seal providing a seal between the center breach housing and the rotating drum members. FIG. 10 shows the rotating seal 232 and the static seal 248 kept in contact by a piston rod 260. The seals prevent the escape of gas from the internal portions of the balling drum and the hardening drum through the center breach. This device, while similar to the present invention, suffers in several ways. The metal-to-metal wear face of this device is variable and not fixed, thus requiring piston rods to constantly hold the seal members together in sealing contact. Further, no graphite inserts are disclosed between the wear faces to ensure constant lubrication of the surfaces. Additionally, this invention only seals the outer shell, not the inner shell, as in the present invention.
GRANDCOLAS et al., U.S. Pat. No. 4,338,080, discloses a seal assembly for a cement manufacturing rotary kiln. The background of the invention states that the internal temperatures of the kiln to be in excess of 1000.degree. C. The seal is comprised of a plurality of contacting graphite elements. The graphite members are held against the surface of the kiln by a flexible clamping cable. The patent also discloses alternative sealing material depending upon the conditions of use. Low density graphite is softer and lessens the possibilities of leaks, but also wears faster in abrasive conditions. Resin impregnated graphites are another alternative depending upon the operating temperature of the seal. This patent discloses seals of graphite or graphite impregnated resins, and not the seal of the present invention. Because the seal of the present invention is comprised of an aluminum-bronze material, it does not suffer the shortcomings of the graphite or graphite impregnated resin of wearing out prematurely due to abrasion and excessive heat.
GRACHTRUP, U.S. Pat. No. 4,457,520, discloses sealing the gap between a rotary kiln and an inlet housing. This invention includes means for sealing the kiln in both the longitudinal and rotational directions. The rotating seal is shown in FIG. 1 as wearing surfaces 15, 15a, 16 and 16a. The wearing surfaces are held in sealing contact by means of pressure. The wearing surfaces are made "from a suitable material." This device suffers in that it requires additional equipment to provide pressure to hold the seals in constant contact. The present invention includes a fixed seal, and thus does not require the added structure and expense of providing longitudinal contacting members or pressure.
HOGAN, U.S. Pat. No. 5,078,836, discloses an apparatus and method for thermally treating feed material, such as solid waste. The apparatus comprises coaxial rotating drums and a rotating spiral insert for advancing the product through the drum. The treating temperatures in the drums are in excess of 1500.degree. F. While the structure of this retort device is similar to the rotating retort heat treating furnace of the present invention, the composition of the seals is not disclosed. However, the background of the invention does note that these seals for sealing such retorts are exposed to high temperatures and subject to failure due to such extreme temperatures.